1. Field of the Invention
The invention relates to a method for regulating a switched-mode power supply having at least one electronic switch and a drive circuit with primary current simulation, in which case, as the output load decreases, the frequency is lowered to reduce switching losses.
The invention furthermore relates to a switched-mode power supply having at least one electronic switch and a drive circuit with primary current simulation, in which case, as the output load decreases, the frequency is lowered to reduce switching losses.
In a switched-mode power supply, a DC voltage is chopped by an electronic switch, for example, a switching transistor, into a square-wave voltage that is transformed using a transformer and subsequently rectified. The output voltage is regulated to a constant value using a regulator that controls the duty ratio or the frequency of the switching operation. Switched-mode power supplies are distinguished by a series of advantages when compared with conventional power supplies. Switched-mode power supplies are embodied as flyback converters, forward converters, or push-pull converters.
In order to reduce switching losses in a switched-mode power supply as the output load decreases, the frequency is lowered in frequency jumps which, however, can cause disturbances in some areas of use. Thus, by way of example, when the frequency is lowered by frequency jumps when a switched-mode power supply is used in a television set, the picture geometry is considerably impaired. Although such disturbances can be reduced by adapting the regulating characteristic, the outlay for this is considerable.
2. Summary of the Invention
It is accordingly an object of the invention to provide a method for regulating a switched-mode power supply and also a switched-mode power supply which overcome the above-mentioned disadvantages of the prior art apparatus and methods of this general type.
In particular, it is an object of the invention to provide a method for regulating a switched-mode power supply and also a switched-mode power supply using simple means without a high outlay in such a way that when the frequency is lowered, disturbances in the load are largely avoided.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for regulating a switched-mode power supply that includes steps of: providing a switched-mode power supply having at least one electronic switch and a drive circuit having an input receiving a primary current simulation, the switched mode power supply supplying a relatively higher output power at times and a relatively lower output power at other times; as an output load decreases, lowering a switching frequency to reduce switching losses; and starting the step of lowering the switching frequency during an occurrence of the lower output power by, during a switch-on interval of the electronic switch, deforming a rise in a voltage at the input for receiving the primary current simulation such that the voltage rises more steeply during a time segment. The object of the invention is achieved by virtue of the fact that the beginning of the lowering of the frequency is shifted toward lower output powers.
In accordance with an added mode of the invention, a resistive coupling network is used to generate the rise in the voltage at the input for receiving the primary current simulation.
In accordance with an added mode of the invention, a capacitive coupling network is used to generate the rise in the voltage at the input for receiving the primary current simulation.
In accordance with another mode of the invention, a switching transistor is used as the electronic switch.
With the foregoing and other objects in view there is also provided, in accordance with the invention, a switched-mode power supply, that includes at least one electronic switch, and a drive circuit having an input for receiving a primary current simulation. The drive circuit reduces a switching frequency to reduce switching losses as an output load decreases. The drive circuit provides a control voltage for the electronic switch. A coupling network couples the control voltage to the input for receiving the primary current simulation. The coupling network is designed to deform a rise in a voltage at the input for receiving the primary current simulation, during a switch-on interval of the electronic switch such that the voltage rises more steeply during a time segment. The object of the invention is achieved virtue of the fact that the control voltage for driving the electronic switch is coupled via a network to the input of the primary current simulation.
In accordance with an added feature of the invention, the coupling network is a resistive resistor network.
In accordance with an additional feature of the invention, the resistor network is a voltage divider including two resistors.
In accordance with another feature of the invention, the power supply includes: a parallel circuit including a first resistor and a first capacitor connected in parallel with the first resistor; a series circuit including a junction point, a second capacitor, and a second resistor connected in series with second resistor at the junction point; a third resistor; a transformer having a primary winding with a first connection and a second connection, the transformer having a secondary winding for connecting to a load to supply current to the load; a third capacitor; a fourth resistor; and a supply voltage and a reference-ground potential. The drive circuit is either the Infineon Technologies module TDA 16846 or the Infineon Technologies module TDA 16847. The module includes a pin 1, a pin 2, and a pin 13. The parallel circuit connects pin 1 of the module to the reference-ground potential. Pin 2 is the input for receiving the primary current simulation. The series circuit connects pin 2 to the reference-ground potential. The electronic switch is a switching transistor having a gate electrode, a source electrode, and a drain electrode. pin 13 of the module is connected to the gate electrode of the switching transistor. The third resistor connects pin 13 of the module to the junction point between the second capacitor and the second resistor. The source electrode of the switching transistor is connected to the reference-ground potential. The drain electrode of the switching transistor is connected to the first connection of the primary winding of the transformer. The second connection of the primary winding of the transformer is connected to the supply voltage. The third capacitor connects the second connection of the primary winding of the transformer to the reference-ground potential. The fourth resistor connects pin 2 of the module to the supply voltage.
In accordance with a further feature of the invention, the switched-mode power supply includes: a parallel circuit including a first resistor and a first capacitor connected in parallel with the first resistor; a transformer having a primary winding with a first connection and a second connection, the transformer having a secondary winding for connecting to a load to supply current to the load; a second capacitor; a second resistor; an RC element including a third resistor and a third capacitor connected in series with the third resistor; a fourth capacitor; and a supply voltage and a reference-ground potential. The drive circuit can be either an Infineon Technologies module TDA 16846 or an Infineon Technologies module TDA 16847. The module includes a pin 1, a pin 2, and a pin 13. The parallel circuit connects pin 1 of the module to the reference-ground potential. Pin 2 is the input for receiving the primary current simulation. The second capacitor connects pin 2 to the reference-ground potential. The electronic switch is a switching transistor having a gate electrode, a source electrode, and a drain electrode. Pin 13 of the module is connected to the gate electrode of the switching transistor. Pin 13 of the module is feedback-connected to pin 2 by the RC-element. The source electrode of the switching transistor is connected to the reference-ground potential. The drain electrode of the switching transistor is connected to the first connection of the primary winding of the transformer. The second connection of the primary winding of the transformer is connected to the supply voltage. The fourth capacitor connects the second connection of the primary winding of the transformer to the reference-ground potential. The second resistor connects pin 2 of the module to the supply voltage.
In accordance with a further added feature of the invention, the coupling network is a capacitive network.
In accordance with a further additional feature of the invention, the capacitive network is an RC element including a resistor and a capacitor connected in series with the resistor.
In accordance with yet an added feature of the invention, the electronic switch is a switching transistor.
With the foregoing and other objects in view there is also provided, in accordance with the invention, a switched-mode power supply that includes: at least one electronic switch having a switch-on interval; a drive circuit having an input for receiving a primary current simulation, the drive circuit reducing a switching frequency to reduce switching losses as an output load decreases; a terminal for receiving a reference-ground potential; a terminal for receiving a supply voltage; and a network connected between the reference-ground potential, the supply voltage, and the input of the drive circuit for receiving the primary current simulation. The network is designed to deform a rise in a voltage at the input during the switch-on interval of the electronic switch such that the voltage rises more steeply during a time segment.
In accordance with an added feature of the invention, the network includes a series circuit with a resistor and a capacitor; the input for receiving the primary current simulation is connected to a reference-ground potential; and the network includes a further resistor connecting the input for receiving the primary current simulation to a supply voltage.
In accordance with an additional feature of the invention, the network includes a series circuit with a resistor, a capacitor, and a parallel circuit having a further resistor and a diode. The parallel circuit connects the input for receiving the primary current simulation to the reference-ground potential. The network includes a further resistor that connects the input for receiving the primary current simulation to the supply voltage.
In accordance with another feature of the invention, the network includes a series circuit having a capacitor and a parallel circuit that is connected in series with the capacitor. The parallel circuit includes a first branch and a second branch connected in parallel with the first branch. The first branch includes a resistor. The second branch includes two diodes that are connected in series. The network includes a further resistor that connects the input for receiving the primary current simulation to a supply voltage.
In accordance with a further feature of the invention, the switched-mode power supply includes: a parallel circuit including a first resistor and a first capacitor connected in parallel with the first resistor; a transformer having a primary winding with a first connection and a second connection; an RC element including a third resistor and a third capacitor connected in series with the third resistor; a fourth capacitor; and a supply voltage and a reference-ground potential. The drive circuit-is either an Infineon Technologies module TDA 16846or an Infineon Technologies module TDA 16847. The module includes a pin 1, a pin 2, and a pin 13. The parallel circuit connects pin 1 of the module to the reference-ground potential. Pin 2 is the input for receiving the primary current simulation. The electronic switch is a switching transistor having a gate electrode, a source electrode, and a drain electrode. Pin 13 of the module is connected to the gate electrode of the switching transistor. Pin 13 of the module is feedback-connected to pin 2 by the RC-element. The source electrode of the switching transistor is connected to the reference-ground potential. The drain electrode of the switching transistor is connected to the first connection of the primary winding of the transformer. The second connection of the primary winding of the transformer is connected to the supply voltage. The fourth capacitor connects the second connection of the primary winding of the transformer to the reference-ground potential.
In accordance with an added feature of the invention, the electronic switch is a switching transistor.
By shifting the beginning of the lowering of the frequency toward lower output powers, the frequency jumps no longer occur in a power range where they cause disturbance, but rather can be shifted in a targeted manner, by skillfully selecting the beginning of the lowering of the frequency, into a power range where they no longer cause disturbance. In circuit terms, this method is realized by coupling the control voltage to the input of the primary current simulation by means of a network. This network may be embodied as a resistive or capacitive network. The network provided according to the invention deforms the voltage rise at the input of the primary current simulation of the evaluation circuit during the switch-on time of the electronic switch in such a way that a definable relationship exists between the frequency and the electrical power via the regulating voltage.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for regulating a switched-mode power supply and a switched-mode power supply, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.